Seems like we need to cut to the chase on solar panels. I think its reasonable to expect that your solar panel charges your battery in a day of full sun. That way you can boondock as long as you want.Here's what you need:

Wait a minute you say, I've been to a bunch of solar web sites and there's charts and graphs and battery sizes and all kinds of stuff. What size panel do I need? Why do I need a controller? How do I wire it? Why did you pick such a small wire, isn't that too small? I have a battery charger, won't that screw things up? And whats that aiming stuff about, don't I have to angle my panel or something?

- Solar Panel Size

Solar panels aren't as efficient as we would hope. You can get a 5W panel because its real cheap but it won't charge your battery, it will just maintain it. Get the largest size you can afford and they aren't cheap. Expect to pay about $6/watt. Don't expect the panel to completely charge the battery in one day (in full sun) if its less than 65W. 85W is better. And don't be a battery hog! Minimize your power usage, treat electricity like water and turn it off as soon as you can. The more juice you use the bigger solar panel you will need. A 65W panel is the smallest you can get and reasonably expect to charge your battery in one day with miserly power usage.

- Battery Size

Wow, there's a lot of debate on this topic. Get a group 27 Deep Cycle battery if you don't want to think about it. Use an online amp-hour calculator if you want to be more precise and get a more exact battery size. But the bottom line is that a 120 amp-hour group 27 battery is about the best choice when it comes to capacity versus cost.

- Controllers

You need a controller so you don't overcharge your battery and ruin it. Small panels don't need a controller but you don't want a small panel because it won't charge your battery in a day. A Sunsaver 10 is a good compromise between cost and efficiency. It's rated for 10A so you can start with an 65 or 85W panel and add another one in the future if you really get into solar power. If you're sure you won't every get another panel you can go with the Sunsaver 6.

- Wiring a Solar Panel

Its easy to wire a solar panel. Two wires from the panel to the controller. Two wires from the controller to the battery. Stick a 15A fuse on the positive wire between the battery and the controller. Keep the fuse as close to the controller as you can. Read the instructions that come with the panel, controller and battery and make sure you follow the polarity marking ( + and -) on each device.

- #12 wire

The power wasted in voltage drop through a 10' section of #12 wire from an 85W solar panel to your battery is about half a watt. Don't worry about it.

- Battery Charger

The Sunchaser controller "knows" if a battery charger is in use and shuts down the panel. It turns it back on if you turn off the battery charger. If its dark outside the panel won't be working anyways. It also "knows" if your charging the battery off the 12V side of a generator and shuts down the panel.

- Aiming

Okay, here's where you have to make some decisions that will affect how much solar panel you buy. You can expect to gain about 20% extra charging capacity if you're real anal and point the panel right at the sun every 30 minutes or so. If you're lazy like me you can just lay the panel flat where it will get full sun and forget about it. Bump the panel sizes shown above up by 20% if you can't be bothered by angling the panel towards the sun. But watch out for any kind of shade on your panel. Just the tiniest, little bit of shading will cripple your panel's output.

Okay, I've been a bit flip about this but I feel like I can be because my solar panel system has worked like a champ and I don't have to worry about battery capacity anymore. There's a ton of technical items that can be discussed about solar panels, and they're all relevant. BUT, I don't believe that it will change the sizes of the items I've posted above by much. And if you're just trying to get into a solar panel system without having to take an engineering course, you can't go wrong with what I've posted. You just might not like the price, but what are you going to do?

Bruce

Last edited by bdosborn on Tue Feb 14, 2012 2:49 pm, edited 4 times in total.

...good stuff Bruce, very useful, without being confusing...have added a link to this, on Steve's new Electrical summary.
madjack

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Bruce what suggestions do you have for those of us that can't run a solar panel like yours because of a Fantastic-fan? I have a 5 watt and it kept our battery in good health but I desire more. Danny

"Conditions are never just right. People who delay action until all factors are favorable do nothing". William FeatherDon't accept "It's Good Enough" build to the best of your abilities.Teardroppers Of Oregon & Washington

My thought have gone there many times, and then, as you say, everything gets too technical and I just forget about it.

This helps a lot.

Thanks._________________sid n side

Sid & All

Both MJ and I agree with you that Bruce takes a sometimes difficult subject of Solar planning for boondocking and honed it down to read in layman terms.

We have a new Electrical Considerations when building a trailer:link that is going to be a living document as time goes forward. In section 4 Solar Power & Controllers: We have put Bruce's info as a link to this thread. We will do this pointing out of valuble information as time goes forward so the information will be in one spot for someone to look to first and then ask more questions they may have.

"A man who is good enough to shed his blood for his country is good enough to be given a square deal afterwards." -------Theodore Roosevelt

halfdome, Danny wrote:Bruce what suggestions do you have for those of us that can't run a solar panel like yours because of a Fantastic-fan? I have a 5 watt and it kept our battery in good health but I desire more. Danny

I don't know why you can't use a panel because of the fan. I have a couple of muffin fans (about a 1 amp load) in my trailer and the panel will run them without a problem *IF* the battery is connected. I've turned on all my electrical stuff, disconnected the battery and the solar panel ran everything, including the fans. It won't start the fans without the battery though, the motor inrush current shuts down the controller. Just get a bigger panel and a good controller like the Sunchaser and you should be able to charge your battery with the fan or just run the fan off the panel in hot weather.
Bruce

bledsoe3 wrote:Bruce, I think what Danny meant was, the fan is smack in the middle of the roof. Hard to mount a solar panel there.

Dohhh! Thanks Jim for pointing out the trees through the forrest.

Danny,

Build a stand for your panel and point it at the sun, with a pigtail to plug it into the trailer. Somebody posted a stand they made out of PVC pipe somewhere around here. Or, you could even just lean it against the trailer. Just make sure it doesn't tip over or grows legs and walks away.
Bruce

Bruce wrote:Somebody posted a stand they made out of PVC pipe somewhere around here. Or, you could even just lean it against the trailer. Just make sure it doesn't tip over or grows legs and walks away.

I have my panel mounted on the galley hatch, just back from the hinge. That way I can point it more directly at the sun by moving the trailer, or I can leave the hatch open as a sun shade which also aims it at the sun. This works well and I don't have to worry about theft, tripping over the wire, etc..